Limited Effect of Systemic β-Blockade on Sympathetic Outflow

Tank, Jens; Diedrich, André; Schroeder, Christoph; Stoffels, Mandy; Franke, Gabi; Sharma, Arya M.; Luft, Friedrich C.; Jordan, Jens

doi:10.1161/hy1201.096120

Cited by 29 publications

(27 citation statements)

References 28 publications

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“…Nerve activity was amplified with a total gain of 100 000, bandpass filtered (0.7 to 2 kHz), full-wave rectified, and integrated. 25 MSNA recordings were accepted as adequate according to the following criteria: (1) pulse synchrony; (2) facilitation during Valsalva straining, and suppression during the hypertensive overshoot after release; (3) increases in response to breath holding; and (4) insensitivity to emotional stimuli.…”

Section: Instrumentationmentioning

confidence: 99%

Baroreflex Regulation of Heart Rate and Sympathetic Vasomotor Tone in Women and Men

et al. 2005

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Abstract-Gender has been reported to influence baroreflex heart rate regulation and baroreflex blood pressure buffering.We tested the hypothesis that gender influences baroreflex regulation of heart rate and sympathetic vasomotor tone. We recruited 32 normal-weight healthy subjects (17 men and 15 women). ECGs for heart rate, brachial and finger blood pressure, and muscle sympathetic nerve activity (MSNA) were measured. Baroreflex heart rate and MSNA regulation were assessed using incremental phenylephrine and nitroprusside infusions. Baseline blood pressure was similar in men and women. MSNA was 21Ϯ2.5 bursts/min in women and 19Ϯ2.8 bursts/min in men (NS). The gain of the baroreflex MSNA curves was similar in women and men (Ϫ1.9Ϯ0.2 bursts/min per mm Hg in men and Ϫ2.0Ϯ0.3 bursts/min per mm Hg in women). Baroreflex gain for heart rate regulation was 17Ϯ3.2 ms/mm Hg in women and 19Ϯ1.9 ms/mm Hg in men (NS). We conclude that baroreflex gains for heart rate and sympathetic MSNA regulation are similar in women and men. However, the probability for congruence between men and women in terms of the MSNA baroreflex curves was 0.06% for burst rate, 0.4% for burst incidence, and 0.01% for burst area. In women, the MSNA baroreflex curve may be shifted to slightly lower blood pressure such that at a given blood pressure MSNA tends to be lower. Key Words: autonomic nervous system Ⅲ baroreflex Ⅲ gender Ⅲ nervous system, sympathetic T he autonomic nervous system influences blood pressure and heart rate through adjustments in parasympathetic and sympathetic activity. Parasympathetic and sympathetic activities are tightly regulated through baroreflex mechanisms. Therefore, baroreflexes have a pivotal role in shortterm cardiovascular regulation and buffer-excessive blood pressure swings. 1,2 Among numerous other variables, baroreflexes are also involved in long-term blood pressure maintenance. [3][4][5] Even when overall blood pressure regulation is functioning properly, the balance between baroreflex regulation of heart rate and vascular tone may be perturbed. Imbalance between sympathetic activation of the heart and the vasculature has been described in heart failure patients, 6 postural tachycardia syndrome patients, 7,8 and in healthy subjects treated with norepinephrine transporter inhibitors. 9,10 Factors influencing baroreflex function may have an important bearing on human cardiovascular disease. Gender may be such a variable. Previous studies suggest that baroreflex blood pressure buffering is less effective in women than in men. 11 The balance between baroreflex-mediated heart rate and muscle sympathetic nerve activity (MSNA) changes may also be influenced by gender. The idea is supported by the observation that resting sympathetic vasomotor tone tends to be decreased in women, 12,13 whereas resting heart rate is increased. 14 -16 Furthermore, with standing, women showed an exaggerated heart rate and an attenuated sympathetic vasomotor response. 17 Moreover, previous studies suggested that baroreflex heart rate regulati...

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Section: Instrumentationmentioning

confidence: 99%

Baroreflex Regulation of Heart Rate and Sympathetic Vasomotor Tone in Women and Men

et al. 2005

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“…Nerve activity was amplified with a total gain of 100 000, bandpass-filtered (0.7 to 2 kHz), and integrated. 15 …”

Section: Instrumentationmentioning

confidence: 99%

α-2 Adrenergic Transmission and Human Baroreflex Regulation

et al. 2004

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Abstract-We observed earlier that central ␣-2 adrenoceptor stimulation in mice greatly augments parasympathetic tone.To test the effects in humans, we assessed autonomic vasomotor tone and baroreflex regulation in 9 normal young adults on 2 occasions, once with and once without clonidine. We determined heart rate (HR), beat-by-beat blood pressure (BP), and muscle sympathetic nerve activity. HR variability was analyzed in the time and frequency domain. Pharmacological baroreflex slopes were determined using incremental phenylephrine and nitroprusside infusions. Clonidine lowered resting BP (122Ϯ4/73Ϯ3 versus 100Ϯ7/55Ϯ3 mm Hg, PϽ0.01), muscle sympathetic nerve activity (18Ϯ3 versus 4Ϯ2 bursts/min, PϽ0.01), and HR (62Ϯ3 versus 56Ϯ3 bpm, PϽ0.05). The baroreflex heart rate curve was reset to much lower HR values and showed no saturation at low HR. HR variability profoundly increased during clonidine plus phenylephrine (total power: 3224Ϯ843 versus 8943Ϯ2329 ms 2 , PϽ0.05). High-frequency power was 1451Ϯ520 at baseline and 6720Ϯ2475 ms 2 during baroreceptor loading (PϽ0.05). The low-frequency/high-frequency ratio decreased (1.94Ϯ0.41 versus 0.69Ϯ0.10, PϽ0.05). In contrast, clonidine reduced resting sympathetic vasomotor tone and shifted the operating point of the sympathetic baroreflex to a flat part of the sympathetic baroreflex curve. The shift decreased the ability of the baroreflex to withdraw sympathetic vasomotor tone during baroreflex loading. These baroreflex changes were associated with a moderate increase in phenylephrine responsiveness. We conclude that ␣-2 adrenoceptor stimulation has a differential effect on baroreflex HR and vasomotor regulation. ␣-2 Adrenoceptor stimulation greatly augments baroreflex-mediated bradycardia, most likely by parasympathetic activation. Key Words: antihypertensive, agents Ⅲ blood pressure Ⅲ heart rate Ⅲ baroreflex Ⅲ sympathetic nervous system C hanges in arterial blood pressure (BP) are sensed by carotid, aortic, and perhaps coronary baroreceptors. 1,2 The signal is integrated in cardiovascular control centers in the brain stem and leads to compensatory adjustments in sympathetic and parasympathetic activity. BP reduction is followed by baroreflex-mediated increases in heart rate (HR) and sympathetic vasomotor tone. 1,3,4 An increase in BP attenuates HR and sympathetic vasomotor tone. 1,3,4 Thus, the baroreflex serves as a buffer to prevent excessive BP swings. 5,6 The buffering function is severely impaired in patients with bilateral damage to baroreceptors or baroreflex afferents (baroreflex failure). 7,8 These patients feature extreme volatility of BP. Neuronal degeneration of sympathetic and parasympathetic efferents is tantamount to autonomic failure. Patients with autonomic failure have severe orthostatic hypotension. 9,10 These rare diseases illustrate the pivotal role of baroreflexes in short-term cardiovascular regulation in humans. Even subtle changes in baroreflex function may elicit important cardiovascular effects. Adrenergic mechanisms in the brain have an impo...

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“…For the central effect, it is possible that systemic application of PRO would lead to sufficient β1-and β2-ADR blockade in the brain, as the central effect of PRO has been evidenced in this study by the concurrent decreases of LF BPV for the reduction of CIP, and in spite of the increase of LF HRV , the increase of HF HRV with decrease of LF/HF for reduction of CIT [16,17,26]. For the periphery effect [19], PRO is known to inhibit β-adrenergic transmission to the heart and attenuate presynaptic β2-ADR to inhibit synaptic NE releases at the postganglionic adrenergic neurons [27]. The peripheral effects of PRO may explain, together with its central effects, the decreases of SBP and HR.…”

Section: Responses Of Cs To Promentioning

confidence: 93%

“…The antihypertensive effect of PRO has been extensively studied, however it still remains unclear [17,19]. It is known that rat has a strong β-ADR tone in the peripheral vascular beds [20].…”

Section: Responses Of Precs To Promentioning

confidence: 99%